Some data storage systems, such as disk drive systems, use a spindle motor to change the position of storage regions with respect to a spindle mechanism for reading and writing to the storage regions. A disk drive data storage system typically includes one or more disks or platters for storing information, and the spindle motor may be used to rotate the platters. Subsequently, a read/write head may read information from or write information to the storage regions on the platters.
In order to accurately position the read/write head with respect to a storage region on a platter, variations in the rotational speed of the platter are kept at a minimum during operation. Specifically, once a spindle motor for rotating the platters has been accelerated to an operational speed, a spindle motor control system is used to maintain the operational speed.
However, external forces or disturbances exist in the disk drive system that would interfere with speed control of the spindle motor. One such disturbance is the repeatable timing run-out (RTRO).